1. Field of the Invention
The present invention relates to an apparatus for forming a radiation source distribution image. The apparatus detects radiation from radiation sources in an examinee to form the distribution image of the radiation sources in the examinee.
2. Description of the Related Art
In nuclear medicine diagnosis, the influence of radiation exposure to an examinee should be considered. For example, when cancer is treated by the radiation to an affected part in the examinee, it is important to know the dose of the radiation to the affected part correctly. Further, it is also important to know the dose of the radiation to normal tissues around the affected part. It is also necessary to know the dose when some radiation sources are inhaled due to an accident, for example, in a nuclear power plant.
Conventionally, the dose of the radiation is estimated by simulation from the quantity of the radiation sources administered to the affected part. However, in the simulation, it is impossible to know the correct dose of the radiation.
In view of the above, for example, a gamma camera apparatus (Anger camera apparatus) has been developed, in which the gamma ray radiated from radiation sources is detected by an NaI(T1) scintillator, and in which a distribution image of the radiation sources in the examinee is formed based on the detected information.
In the conventional gamma camera apparatus, the detector is rotated around the examinee in order to obtain a tomographic image of the examinee. Therefore, the apparatus is large, and it has been necessary to provide a dedicated bed or cot which is integrated with the apparatus into one unit.
Under these circumstances, a gamma camera apparatus with a coded aperture plate arranged in front of a scintillator has been suggested. The coded aperture plate has a large number of apertures formed in accordance with a predetermined array rule. A three-dimensional distribution image of the radiation sources in an examinee is formed based on the information obtained by the scintillator using the coded aperture plate (see “Coded Aperture Emission CT using M array”, Transactions of the Society of Instrument and Control Engineers, Vol. 28, No. 4,426/432 (1992), and “Three-dimensional reconstruction of 99mTc distribution by using coded aperture CT”, Instrument department of the Society of Instrument and Control Engineers, 17th sensing forum (2000)).
When using the gamma camera apparatus with the coded aperture plate, it is possible to obtain the distribution image of the radiation sources without rotating a detector around the examinee. Therefore, it is possible to downsize the apparatus.